Final answer:
a. Francium oxide (Fr2O)
The most predictable product when burning francium in air is francium oxide (Fr2O), due to the behavior of alkali metals reacting with oxygen to form oxides.
Step-by-step explanation:
The product of burning francium in air is likely to be francium oxide (Fr2O), option (a). While no direct reaction of francium burning in air has been recorded due to its extreme rarity and radioactivity, we can make an educated guess based on the behavior of other alkali metals in the same group.
Alkali metals typically react with oxygen to form oxides, and the reaction usually results in the metal being in its +1 oxidation state paired with oxygen in a -2 state, forming an M2O compound. Therefore, as francium is an alkali metal, the most predictable product when Francium burns in air would be its oxide, Fr2O.